1. Field of the Invention
This invention relates to an amorphous alkali metal silicate compound with multiple-cycle washing performance which may be used as a water-soluble builder in detergents or cleaning formulations and to the use of such alkali metal silicate compounds in detergents or cleaning formulations, to extruded detergents or cleaning formulations and to a process for their production.
Modern compacted detergents or cleaning formulations generally have the disadvantage that, on account of their compact structure, they show poorer solubility in aqueous liquors than, for example, lighter spray-dried detergents or cleaning formulations of the prior art. Detergents or cleaning formulations generally tend to show a poorer dissolving rate in water, the higher their degree of compaction. Zeolites which are typically present as builders in detergents or cleaning formulations can make an additional contribution to the impaired dissolving behavior on account of their insolubility in water.
A water-soluble alternative to zeolite are amorphous alkali metal silicates with multiple-cycle washing performance.
2. Discussion of Related Art
It is known that powder-form hydrated water-soluble silicates still containing around 20% by weight of water can be obtained by spray drying 20 or roll drying of waterglass solutions (cf. Ullmanns Enzyclopadie der technischen Chemie, 4th Edition 1982, Vol. 21, page 412). Products such as these are commercially available for various purposes. Corresponding powders have a very loose structure as a result of spray drying, their apparent densities generally being well below 700 g/l.
Granular alkali metal silicates with higher apparent densities can be obtained in accordance with the teaching of European patent application EP-A-0 526 978. In the process disclosed in this document, an alkali metal silicate solution with a solids content of 30 to 53% by weight is introduced into a heated drum about the longitudinal axis of which rotates a shaft comprising a plurality of arms extending close to the inner surface of the drum, the drum wall having a temperature of 150 to 200.degree. C. and the drying process being supported by a gas introduced into the drum with a temperature of 175 to about 250.degree. C. This process gives a product with a mean particle size of 0.2 to 2 mm. A preferred drying gas is heated air.
European patent application EP-A-0 542 131 describes a process in which a product completely soluble in water at room temperature with an apparent density of 500 to 1200 g/l. Heated air is preferably used for drying. This process is also carried out using a cylindrical dryer with a heated wall (160 to 200.degree. C.), about the longitudinal axis of which a rotor with vane-like blades rotates at such a speed that a pseudoplastic paste with a free water content of 5 to 12% by weight is formed from the silicate solution with a solids content of 40 to 60% by weight. The drying process is supported by a hot air stream (220 to 260.degree. C.).
Earlier hitherto unpublished patent application P 44 19 745.4 also describes a water-soluble, amorphous and granular alkali metal silicate which is produced similarly to the method described in EP-A-0 526 978, but which contains silica. By "amorphous" is meant "X-ray amorphous". This means that, in X-ray diffractograms, the alkali metal silicates do not produce any sharp reflexes, but at best one or more broad maxima of which the width amounts to several degrees of the diffraction angle. However, this does not mean that zones producing sharp electron diffraction reflexes would not be found in electron diffraction experiments. This may be interpreted to mean that the substance has microcrystalline zones up to about 20 nm (max. 50 nm) in size.
Granular amorphous sodium silicates obtained by spray drying of aqueous waterglass solutions, subsequent grinding and subsequent compaction and spheronizing accompanied by additional drying of the ground material are the subject of U.S. Pat. Nos. 3,912,649, 3,956,467, 3,838,193 and 3,879,527. The products obtained have a water content of around 18 to 20% by weight for apparent densities well above 500 g/l.
Other granular alkali metal silicates with multiple-cycle washing performance are known from European patent applications EP-A-0 561 656 and EP-A-0 488 868. The products in question are compounds of alkali metal silicates with certain Q distributions and alkali metal carbonates. These compounds are produced by granulating powder-form water-free sodium carbonate in the presence of a sodium silicate solution (waterglass solution) and drying the products obtained in such a way that they have a certain residual water content bound to the silicate.
German patent application DE-A-44 06 592 describes absorbent alkali metal silicate compounds which are present in the form of a multicomponent mixture and which have been produced by spray drying of an aqueous preparation of the multicomponent mixture with superheated steam. Compounds such as these may be used as supports for liquid preparations of--in particular--surfactants.
European patent application EP-A-0 219 314 describes spray-dried high-surfactant granules containing (a) 30 to 60% by weight of a mixture of alkyl benzene sulfonate and C.sub.12-16 alkyl sulfate in a ratio by weight of 4:1 to 1:4 and (b) alkali metal silicates in a ratio by weight of (a) to (b) of 1.5:1 to 6:1.
EP-A-0 651 050 describes a process for the production of agglomerates in which a salt, for example a silicate or carbonate, is processed with a water-containing "binder" which contains at least 20% by weight of silicate and at least 30% by weight of anionic surfactant.
European patent EP 486 592 describes a process for the production of high-density extrudates in which a solid free-flowing compound is extruded under pressure in strand form. The solid free-flowing compound contains a plasticizer and/or lubricant of which the effect is that the compound softens plastically under the pressure or the introduction of specific energy and thus becomes extrudable. After leaving the multiple-bore die, no further shear forces act on the system so that the viscosity of the system increases to such an extent that the extruded strand can be cut to predetermine extrudate dimensions. Now, it is known from International patent application WO-A-94/09111 that the compound to be extruded must contain both constituents which show pseudoplastic behavior and constituents which exhibit dilatant properties. If the compound were only to contain pseudoplastic constituents, it would soften to such an extent (even becoming almost liquid) under the effect of the pronounced shear gradient that the strand would no longer be cuttable after leaving the multiple-bore die. Accordingly, dilatant constituents are used which show increasing plasticity at increasing shear rates and which thus guarantee the cuttability of the extruded strand. Most ingredients of detergents or cleaning formulations show pseudoplastic behavior. Dilatant behavior is more the exception. However, there is one typical ingredient of conventional detergents or cleaning formulations which does show dilatant properties, namely the water-insoluble alumosilicates, such as zeolite, used as builders and phosphate substitutes. Although extruded detergents or cleaning formulations containing 19% by weight of zeolite (based on water-free active substance), 12.5% by weight of sodium carbonate and 2.2% by weight of amorphous sodium silicate are known from International patent application WO-A-94/09111, it was not known that zeolite could be partly or even completely replaced from the point of view of process technology by water-soluble inorganic builders, such as amorphous alkali metal silicates, providing they are used in a certain form. It has been found in this connection that some alkali metal silicate compounds with multiple-cycle washing performance lose some of that performance when processed under the effect of water, powerful shear forces and/or (slightly) elevated temperatures.
One of the problems addressed by the present invention was to provide water-soluble builders for the partial or complete replacement of zeolite in detergents or cleaning formulations so that the dissolving behavior, particularly of heavy detergents or cleaning formulations, would be improved. In addition, these water-soluble builders would also have the capacity to absorb ingredients of detergents or cleaning formulations that are liquid to wax-like at the processing temperature. The invention also set out to provide builders which would not lose their multiple-cycle washing performance, even during processing. Another problem addressed by the present invention was to provide extruded detergents or cleaning formulations which would contain the water-soluble builders to the extent that there would be little or no need for zeolite either from the performance point of view or from the point of view of process technology and a process for the production of these extruded detergents or cleaning formulations.